- ID:
- ivo://CDS.VizieR/J/A+A/508/1527
- Title:
- SiII Radiative transition rates
- Short Name:
- J/A+A/508/1527
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This work reports on radiative transition rates and electron impact excitation collision strengths for levels of the 3s^2^3p, 3s3p^2^, 3s^2^4s, and 3s^2^3d configurations of Si II. The radiative data were computed using the Thomas-Fermi-Dirac-Amaldi central potential, but with the modifications introduced by Bautista (2008, J. Phys. B: Atom. Mol. Opt. Phys., 41, 065701) that account for the effects of electron-electron interactions. We also introduce new schemes for the optimization of the variational parameters of the potential. Additional calculations were carried out with the Relativistic Hartree-Fock and the multiconfiguration Dirac-Fock methods. Collision strengths in LS-coupling were calculated in the close coupling approximation with the R-matrix method. Then, fine structure collision strengths were obtained by means of the intermediate-coupling frame transformation (ICFT) method which accounts for spin-orbit coupling effects.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/566/A105
- Title:
- SiIX K-shell energy levels and transitions
- Short Name:
- J/A+A/566/A105
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Accurate atomic data are needed to analyze the SiIX K-shell features in astrophysical X-ray spectra. Relative large discrepancies in the existing atomic data have impeded this progress. We present the accurate SiIX K-shell transition data, including K-shell energy levels, wavelengths, radiative rates, and oscillator strengths. The flexible atomic code (FAC), which is a fully relativistic atomic code with configuration interaction (CI) included, was employed to calculate these data. To investigate the CI effects, calculations with different configurations included were carried out. The K-shell atomic data of SiIX transitions between 1s^2^2s^2^2p^2^, 1s^2^2s2p^3^, 1s^2^2p^4^, 1s2s^2^2p^3^, 1s2s2p^4^, and 1s2p^5^ are reported. The accuracy of our data is demonstrated by comparing them with the available experimental measurements and theoretical calculations. The energy levels are accurate to 3.5eV, the wavelengths to within 15m{AA}. For most transitions, the radiative rates an accuracy of 20%. The effects of CI from high-energy configurations were investigated as well.
- ID:
- ivo://CDS.VizieR/J/A+A/585/A26
- Title:
- Silicon isoelectronic sequence data
- Short Name:
- J/A+A/585/A26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Multiconfiguration Dirac-Hartree-Fock (MCDHF) calculations and relativistic configuration interaction (RCI) calculations are performed for states of the 3s^2^3p^2^, 3s3p^3^ and 3s^2^3p3d configurations in the Si-like ions Ti IX - Ge XIX, Sr XXV, Zr XXVII and Mo XXIX. Valence and core-valence electron correlation effects are accounted for through large configuration state function expansions. Calculated energy levels are compared with data from other calculations and with experimental data from the reference databases. Lifetime and transition rates along with uncertainty estimations are given for all ions. Energies from the calculations are in excellent agreement with observations and computed wavelength are almost of spectroscopic accuracy, aiding line identification in spectra.
- ID:
- ivo://CDS.VizieR/J/A+A/627/A16
- Title:
- Silicon K-edge dust absorption cross sections
- Short Name:
- J/A+A/627/A16
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The composition and properties of interstellar silicate dust are not well understood. Inthe X-rays, interstellar dust can be studied in detail, by making use of the fine structure features inthe Si K-edge. The features in the Si K-edge offer a range of possibilities to study silicon-bearingdust, such as investigating the crystallinity, abundance and the chemical composition along a given line of sight. We present newly acquired laboratory measurements of the silicon K-edge of several silicate-compounds which complement our measurements from our earlier pilot study. The resulting dust extinction profiles serve as templates for the interstellar extinction that we observe. The extinction profiles were used to model the interstellar dust in the dense environments of the Galaxy. The laboratory measurements, taken at the Soleil synchrotron facility in Paris, were adapted for astrophysical data analysis and implemented in the SPEX spectral fitting program. The models were used to fit the spectra of nine low-mass X-ray binaries located in the Galactic center neighborhood in order to determine the dust properties along those lines of sight. In most lines of sight can be well fitted by amorphous olivine. We also established upper limits on the amount of crystalline material that the modeling allows. We obtained values of the total silicon abundance, silicon dust abundance and depletion along each of the sightlines. We find a possible gradient of 0.06+/-0.02dex/kpc for the total silicon abundance versus the Galactocentric distance. We do not find a relation between the depletion and the extinction along the line of sight.
- ID:
- ivo://CDS.VizieR/J/A+A/549/A128
- Title:
- Singly deuterated isotopologues of formamide
- Short Name:
- J/A+A/549/A128
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Formamide (HCONH_2_) is the simplest molecule with a peptide bond detected in the interstellar medium. One of the keys for understanding the mechanisms for forming formamide in massive hot cores is the comparison of the relative abundances of its deuterated isotopologues. No deuterated species of formamide have been detected to date mostly owing to the lack of laboratory spectral data, which is limited by cm-wave measurements up to 40GHz. Therefore, we decided to extend the measurements and the analysis of the rotational spectra of deuterated isotopologues of formamide into terahertz range. We measured the rotational spectra of deuterated formamide in the frequency range 150-950GHz using the Lille fast-scan and solid-state source spectrometers. The ground vibrational states of 4 different isotopologues of formamide, DCONH_2_, cis-HCONHD, trans-HCONHD, and HCOND_2_ were assigned and analysed. The sets of the rotational and centrifugal distortion constants we obtained allow us to calculate accurate predictions of the transition frequencies for deuterated formamide in the frequency range above 1THz and at least for J<65 and Ka<25.
- ID:
- ivo://CDS.VizieR/J/A+A/321/293
- Title:
- SiO production in interstellar shocks
- Short Name:
- J/A+A/321/293
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the production of SiO in the gas phase of molecular outflows, through the sputtering of Si-bearing material in grains. The sputtering is driven by neutral particle impact on charged grains in C-type shocks, at the speed corresponding to ambipolar diffusion. Shock speeds in the range 10<v_s_<40km/s and preshock densities 10^4^<n_H_<10^7^cm^-3^ have been investigated. Sputtering of Si-bearing material in both the cores and the mantles of the grains is considered. We find that, for v_s_ of approximately 25km/s and n_H_ of the order 10^5^cm^-3^, column densities of SiO similar to those observed in molecular out flow regions can be generated by either mechanism. Impact by particles heavier than helium dominates the core-sputtering process for shock velocities of this order. The profiles of rotational transitions of SiO are computed and compared with observations of molecular outflows.
627. SiS line list
- ID:
- ivo://CDS.VizieR/J/ApJ/690/L122
- Title:
- SiS line list
- Short Name:
- J/ApJ/690/L122
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Spitzer spectra of S stars, which are cool evolved stars with a C/O ratio near unity, some of which have enhanced s-process abundances. We present the detection of a strong and unusual band in the mid-infrared, at 13um, within the N-band window. Using quantum-chemically calculated line lists, and model spectra, we identify this band as the fundamental rovibrational band of SiS. Detection of the overtone band at 6.7um confirms the identification Fitting the line profile shows that the molecule is located in relatively cool layers, at T~1500K. We discuss these results in the context of chemical equilibrium models. The observed strength of these bands in the cool S stars makes them a promising observational diagnostic tool for studying the atmospheres of brown dwarfs and exoplanets.
- ID:
- ivo://CDS.VizieR/J/MNRAS/387/871
- Title:
- SiVI atomic data and broadening effect
- Short Name:
- J/MNRAS/387/871
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Energy levels, electric dipole transition probabilities and oscillator strengths in five times ionized silicon have been calculated in intermediate coupling. The present calculations were carried out with the general purpose atomic structure program superstructure. The relativistic corrections to the non-relativistic Hamiltonian are taken into account through the Breit-Pauli approximation. We have also introduced a semi-empirical correction [term energy corrections (TEC)] for the calculation of the energy levels. These atomic data are used to provide semiclassical electron-, proton- and ionized helium-impact linewidths and shifts for 15 Si VI multiplet. Calculated results have been used to consider the influence of Stark broadening for DO white dwarf atmospheric conditions.
- ID:
- ivo://CDS.VizieR/J/A+A/592/A135
- Title:
- SiXIII and SXV collision strengths
- Short Name:
- J/A+A/592/A135
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Emission lines from highly-excited states (n>=5) of H- and He-like ions have been detected in astrophysical sources and fusion plasmas. For such excited states, R-matrix or distorted wave calculations for electron-impact excitation are very limited, due to the large size of the atomic basis set needed to describe them. Calculations for n>=6 are also not generally available. We study the behaviour of the electron-impact excitation collision strengths and effective collision strengths for the most important transitions used to model electron collision dominated astrophysical plasmas, solar, for example. We investigate the dependence on the relevant parameters: the principal quantum number n or the nuclear charge Z. We also estimate the importance of coupling to highly-excited states and the continuum by comparing the results of different sized calculations. We provide analytic formulae to calculate the electron-impact excitation collision strengths and effective collision strengths to highly-excited states (n>=8) of H- and He-like ions. These extrapolated effective collision strengths can be used to interpret astrophysical and fusion plasma via collisional-radiative modelling.
- ID:
- ivo://CDS.VizieR/J/A+A/522/A103
- Title:
- Si XI K-shell energy levels and radiative rates
- Short Name:
- J/A+A/522/A103
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Atomic data for K-shell transitions are essential for modeling the K absorption lines, which have been observed in the spectra of active galaxies by high-resolution X-ray observatories, e.g. XMM, Chandra, and Suzaku. These accurate atomic data are also needed for line identifications and spectroscopic diagnostic of plasmas in laboratory generated by laser or beam-foil method.The atomic code Flexible Atomic Code (FAC) has been used to calculate these data. Relativistic effects and configuration interactions are taken into account in calculations.The K-shell transitions among the configurations of 1s^2^2s^2^, 1s^2^2s2p, 1s^2^2p^2^, 1s^2^2sn'l', 1s^2^2pn'l', 1s2s^2^2p, 1s2s2p^2^, 1s2p^3^, 1s2s2pn'l' and 1s2p^2^n'l', n'<=4, l'<=n' for beryllium-like Si XI have been calculated. The K-shell energy levels, wavelengths, radiative rates and oscillator strengths for Si XI are reported. In order to assess the accuracy of current data, comparison between our results with former experiments and other theoretical works have been made.
